1. Field of the Invention
The present invention generally relates to coreless and brushless direct-current motors, Gifford McMahon (GM) cryogenic coolers, pulse tube cryogenic coolers, cryopumps, Magnetic Resonance Imaging (MRI) apparatuses, Superconducting Magnet (SCM) apparatuses, Nuclear Magnetic Resonance (NMR) apparatus, and cryogenic coolers for cooling semiconductors.
More particularly, the present invention relates to a coreless and brushless direct-current motor used as a power source of a Stirling type cryogenic cooler or the like. The Stirling type cooler is used for a closed circuit cooling system or the like and has a sealing container that receives an expansion unit and a compressor, a GM cryogenic cooler, a pulse tube cryogenic cooler, a cryopump, a MRI apparatus, a SCM apparatus, an NMR apparatus, and a cryogenic cooler for cooling a semiconductor having the coreless and brushless direct-current motor as a power unit.
2. Description of the Related Art
When a cryogenic cooling apparatus using a gas compressor or gas expanding device such as a Stirling type cryogenic cooler is manufactured and assembled or continuously operated, operation gas or contaminant gas such as moisture or carbon dioxide from components is generated.
In addition, when an electric motor is used as a driving source, contaminants are generated from, for example, a core part, a varnish, or a wire coating in an electric motor part.
In order to prevent influence of these contaminants, a structure where a cup-shaped barrier configured to provide gas-tight isolation between a coil winding and a rotor is provided so as to come in contact with an electric motor used as a driving source, is suggested in U.S. Pat. No. 4,769,997. More specifically, as a cored motor, a single stator (armature) and a driving electric part are arranged outside of a casing partitioned by a non-magnetic cup-shaped cover and a magnetic rotor is completely isolated from the outside environment.
In addition, a Gifford McMahon (GM) cryogenic cooler and a pulse tube cryogenic coolers wherein an electric motor is used as a driving source is suggested in U.S. Pat. No. 5,361,588.